The present invention relates generally to liquid crystals, and more particularly to nematic liquid crystals.
The public's growing demand for the superior image quality provided by high definition televisions (HDTVs) has resulted in ongoing growth of HDTV sales. To compete in today's market, a display needs to meet three main criteria: high contrast, good viewing angle and fast response times. Vertically Aligned Nematic (VAN) Liquid Crystal Displays (LCDs) have inherently high contrast and, with some simple modifications, good viewing angle. Due to their excellent high contrast relative to twisted-nematic (TN) LC displays (familiar in laptop computers, for example), VAN-LCDs dominate the market in large-size LCD panels for high definition televisions (HDTVs). However, the very high contrast of VAN-LCDs comes at the expense of the response time of the display: a pixel in a current VAN display requires approximately 100 ms to switch (rise-time+fall-time), compared to less than 20 ms for a TN display.
Some attempts have been made to improve the switching speed of a VA display by adding a small amount of reactive monomer within the liquid crystal and polymerizing during processing. Although polymer-stabilized vertical-alignment (PS-VA) technology improves the switching speed in HD LCD, there are drawbacks to current PS-VA technology. Current PS-VA technology introduces a difficult irradiation step during processing to induce polymerization of the monomer, which requires precise control of the uniformity and the duration of UV irradiation. Also, the radical and ionic species created during UV radiation have long-term deleterious effects on the LCD (such as increasing the power consumption and reducing the display lifetime).
There is a need for vertically aligned nematic liquid crystal systems having faster response times without sacrificing contrast.